Capping N-Donor Ligands Modulate the Magnetic Dynamics of DyIII β-Diketonate Single-Ion Magnets with D4d Symmetry

A family of four mononuclear Dy-III beta-diketonate complexes with formulas [Dy(tmhd)(3)(Br-2-bpy) (1), [Dy(tmhd)(3)(Br-bpy)] (2), [Dy(tmhd)(3)(dppz)] (3), and [Dy(tmhd)(3)(mcdpq)] (4) (tmhd=2,2,6,6-tetramethyl-3,5-heptanedione, Br-2-bpy=5,5-dibromo-2,2-bipyridine, Br-bpy=5-bromo-2,2-bipyridine, dppz=dipyrido [3,2-a:2,3-c]phenazine, mcdpq=2-methoxyl-3-cyanodipyrido[3,2-f:2,3-h]quinoxaline) were prepared by modifying the capping N-donor coligands. Dy-III centers in these complexes feature an N2O6 octacoordinate environment with distorted square-antiprismatic D-4d symmetry. Magnetic investigations evidenced single-ion magnet behavior in all complexes with energy barriers U-eff of 42.10 (1), 61.47, (2), 77.53 (3), and 2.51K (4) in the absence of static field, as well as 206.03 (1), 224.13 (2), 247.76 (3), and 49.70K (4) under applied dc field (H-dc=1500Oe for 1 and 2; H-dc=1200Oe for 3 and 4). The different natures of the N-donor ligands induce changes in both the coordination geometry and their intermolecular interactions, which severely impact their magnetic dynamics. The disparities in their magnetic behaviors and the uniaxial anisotropies are also explained and substantiated by theoretical calculations.